Philippine authorities urged people in affected coastal regions to move to higher ground after the offshore quake hit south of General Santos, a city of about 720,000.
A series of powerful aftershocks rocked the area from about two hours after the first quake, according to the United States Geological Survey, with the largest measuring 6.5 on the Richter scale.
Videos posted to social media and verified by AFP showed a shopping centre with a Jollibee fast food restaurant reduced to rubble General Santos City, while a school building that officials said was unoccupied crumpled in another.
“Lord, it has really collapsed! … The building has really collapsed!” someone can be heard shouting as the school structure toppled.
The Pacific Tsunami Warning Center said in a notice that tsunami waves were possible “within the next three hours” along the coasts of the Philippines, Indonesia, Palau, Taiwan and Papua New Guinea.
Police Major Roland Catoburan told AFP two people had been crushed to death by a collapsing wall in Alabel, a municipality near General Santos City.
“We have casualties. A wall fell on them,” he said, adding officers were not being allowed to re-enter their stations, some of which now had cracked walls.
Master Sergeant Robert Dagon of the General Santos City police separately confirmed another reported death and four injuries.
“Many buildings were affected, but I cannot enumerate them now because we are busy with ongoing rescues,” Dagon said.
Evacuate now
Philippine President Ferdinand Marcos suspended classes in affected areas of Mindanao island on what was to have been the first day of school, while calling on residents in coastal areas to evacuate immediately.
“Move to higher ground now. Do not wait,” he said. “Your life is more important than anything left behind.”
In Kiamba, a coastal town near the epicentre, about 50,000 residents had already done so.
“As of now, 80 percent of the population has moved to higher ground,” Agripino Dacera, the regional disaster chief said.
“All the villages along the coast were instructed to proceed to evacuation centres.”
The airport in General Santos was also closed until further notice, officials said.
Monday’s quake triggered evacuation warnings for coastal areas of neighbouring Indonesia and Malaysia, with Jakarta’s meteorological agency subsequently lifting its alert.
Japanese authorities issued a tsunami advisory for swathes of its Pacific coast, projecting waves of up to one metre (three feet) to hit different regions from 11:30 am local time (0230 GMT).
Earthquakes are a near-daily occurrence in the Philippines, which is situated on the Pacific “Ring of Fire”, an arc of intense seismic activity stretching from Japan through Southeast Asia and across the Pacific basin.
Eastern Mindanao was rocked by a pair of earthquakes of 7.4 and 6.7 magnitude in October that killed at least eight people.
These followed a magnitude 6.9 quake days earlier that killed 76 people and destroyed or damaged 72,000 buildings in Cebu province in central Philippines, according to government figures.
